As an inexpensive and noninvasive technique, ultrasound is useful as a medical imaging modality able to provide real time feedback in a two-dimensional fashion at a patient's bedside. Ultrasound facilitates dozens of procedures performed in hospitals and clinics every day, with these procedures ranging from breast biopsies to central line catheter insertion to amniocentesis.
In a typical ultrasound guided procedure, a doctor will place a small, handheld probe known as a transducer on a patient's skin. The transducer converts electrical energy to acoustic energy. Acoustical energy is transmitted from the transducer and into the patient's body in the form of sound waves. The transmitted sound waves are either reflected back towards the transducer or absorbed by the medium, depending on the acoustical impedance. For example, a bone or fat, having relatively high acoustical impedance, reflects the sound waves with little or no attenuation of the sound wave, while a vein or artery, having a relatively low impedance, will absorb acoustical energy. The reflected sound waves are converted into electrical signals which are used to form a real time two-dimensional image of a portion of the patient's body.
This image may be used to assist a health professional with locating a region of the patient's body for purposes of locating the point where an invasive medical device, e.g., a needle, is inserted. After locating the correct insertion point, the health professional may then begin the medical procedure, such as insertion of a catheter, administration of a local anesthetic, or removal of tissue as in a biopsy.
It is sometimes difficult to accurately track the path and position of the medical device after it has entered the patient's body on the monitor. The medical device, e.g., a needle, is not typically visualized by the ultrasound image, which is essentially a two-dimensional image. Unless the needle is positioned exactly in-plane with the image, the needle is not visible or only partially visible, which means that the needle location or, more importantly the location of the needle tip, is not known exactly. As such, a health professional will often make numerous attempts to insert the device before he or she can see the target tissue mass or blood vessel buckle under the force of the needle pressing against it. And in the case where the target is, for example, a nerve, the health professional often times can only estimate the location of the needle end if it is not visible on the ultrasound image. Such an error-prone, user-dependent procedure is painful for the patient, time consuming for the health professional, and incurs possible additional liability for the hospital with each use. Procedures for using an ultrasound imaging device for peripheral nerve blocks are described in Anna Dabu BScH, and Vincent W S Chan, M D, FRCPC A Practical Guide to Ultrasound Imaging For Peripheral Nerve Blocks (copyright 2004 by Vincent W S Chan, M D, FRCPC), the contents of which are incorporated herein by reference in its entirety.
There are multi-planar ultrasound imaging devices capable of producing a three-dimensional image of the body, which may be capable of more accurately locating the position of an invasive medical device, but these types of devices are typically expensive to operate, and require a relatively high degree of skill and training to operate. It would be desirable if a low-cost device, capable of being used effectively by a health professional with moderate or little training in ultrasound imaging techniques, were available which could accurately locate the position of the medical device beneath the skin. This would eliminate much of the “guesswork” that is involved in locating a medical device at the point of interest.
Existing ultrasound devices can be characterized by the approach of the needle-guided insertion with respect to the plane of the ultrasound beam. In the “transverse” type, the medical device, e.g., needle, is orientated out of plane and is sometimes disfavored because visualization of the needle is not reliable as it passes through the patient's body. The “longitudinal” type has the added advantage of seeing the entire length of the needle because it is inserted in plane with the ultrasound beam; however, it can be difficult to keep the needle in the plane of the transducer image due to operator skill and inherent needle-bending when passing through tissue.
While the longitudinal type device is preferred because there is greater chance of tracking the needle, it is also more difficult to position the needle at the target when the needle is planar with the image. A transverse needle pathway, on the other hand, is more intuitive, is shown to be easier for novice ultrasound users, and is the preferred approach for various procedures according to experts. The following three studies have been conducted which compare the performance of longitudinal verses transverse type of ultrasound guidance devices, all of which are incorporated herein by reference: P. Marhofer, M. Greher and S. Kapral, Ultrasound guidance in regional anesthesia, British Journal of Anasthesia 94 (1): 7-17 (2005); M. Blaivas, L. Brannam, and E. Fernandez, Short-axis verses Long-axis Approaches for Teaching Ultrasound-guided Vascular Access on a New Inanimate Model, ACAD Emerg Med, Vol. 10, No. 12 (December 2003); and B. D. Sites, J. D. Gallagher, J. Cravero, J. Lundberg, and G. Blike The Learning Curve Associated With a Simulated Ultrasound-Guided Interventional Task by Inexperienced Anesthesia Residents, Regional Anesthesia and Pain Medicine, Vol. 29, No. 6 (November-December 2004), pp. 544-548.
One known ultrasound device for assisting a health professional with needle placement in a body is the ilook™ personal imaging tool, sold by SonoSite, Inc., which includes a series of removable needle guides. The device is used to place a needle at a target location beneath the skinline by real-time visual identification of the target via an ultrasonic image. A bracket, located on the front of the transducer, is used to mount a needle guide. The needle guide is orientated such that a needle received therein will extend approximately perpendicular to the sonic scanning plane. Thus, the SonoSite, Inc. device is a transverse-type device. When it is time to perform the procedure, the device is wrapped in a sterile sleeve (an acoustic coupling gel is put into the sleeve and the sleeve is placed over the transducer) and the sleeve is sealed using a rubber band. The sleeve covers the transducer and bracket. The procedure for use includes inserting the acoustic coupling gel into the sleeve, covering the device with the sleeve, ensuring there are no cuts or tears in the sleeve, then securing the sleeve with a rubber band. After this sterilization of the transducer, a sterile needle guide is snap-fit on the bracket. There is more than one-type of needle guide to choose from. The choice depends upon the distance between the skinline and the top of the vessel. Three choices are available for this particular device: a 1 cm, 2 cm and 3 cm needle guide that reflect an approximate depth of the target vessel beneath the skinline. These different lengths correspond respectively to increasing angular inclinations of the needle relative to the skinline.
The needle guide has a door that can be locked in a closed position by a slidable switch, thereby retaining the needle shaft between the door and a semi-circular recessed area. The needle is placed in this recessed area and the door is closed to hold the needle therein. The transducer with needle is then placed on the skinline and the top of the vessel is located via the sonic image. The needle is then inserted into the body.
After the needle has reached the target, the transducer needs to be removed from the needle, which requires unlatching the door of the needle guide. This procedure can cause complications as it is often necessary to maintain precise positioning of the needle within the body. When the door is being unlatched, there can be unacceptable motion of the transducer (and therefore of the needle) as a result of overcoming mechanical resistance in the latch.
Another known ultrasound imaging device is the Site-Rite® Ultrasound System by Bard Access Systems. This device also provides a needle guide to hold the needle at a fixed angle with a transverse approach and is operated in a similar manner as the SonoSite, Inc. device described above. A health professional first places the transducer such that a target of interest (e.g. a vessel's lumen) is visible on the screen. The location of the target is then estimated and a needle guide is selected such that the needle will pass closest to the target's location. Because the entire probe is enclosed in a sterile sleeve, the needle guide is typically disposable and kept sterile until use. When needed, the needle guide is clamped to the probe through the sterile sleeve. Each needle guide is set to a static angle which is not adjustable. If the insertion angle needs to be corrected, the needle guide must be removed and substituted with a different needle guide. Additionally, after inserting the needle into the target, the probe must be rocked to pry the needle from the needle guide, potentially disrupting the needle-target interaction. This is because the needle guide is a one piece needle guide with lips that are flexed to release the probe from the needle.
U.S. Pat. No. 6,695,786 discloses a longitudinal-type ultrasound device for biopsy procedures. The device has a biopsy needle guide coupled to an ultrasound probe. The needle guide has a needle holder connected to the probe by a link assembly that allows a user to rotate the biopsy needle, but without allowing the user to twist or bend the needle outside the imaged plane. Other examples of longitudinal-type devices are described in U.S. Pat. No. 4,058,114 and U.S. Pat. No. 4,346,717.
Known ultrasound monitors are typically fixed to a stand. In these systems, a health professional often must turn his or her head to focus on the screen. Also, these devices have cords connecting the ultrasound probe to the monitor which are typically much longer than needed for most procedures because it must be sufficiently lengthy for extreme cases. As a result, the cord can often obstruct the probe's user. Additionally, the probe cannot be maintained in a sterile condition when it is placed on a holder provided with the system.
There is a need for a user-friendly ultrasound system that requires only a relatively low-degree of training and/or skill in ultrasound imaging techniques. It would also be desirable to have a device that reduces the error rate and/or discomfort to the patient when locating targets during invasive procedures, and that offers health professionals the ability to direct needles to a target of any depth when the needle is controlled in a plane perpendicular to the scanning plane. It would also be desirable to have a device that is capable of being used in any invasive procedure without additional health costs charged by a health provider; a device that can be pre-aimed at a target and before insertion into a living body; a device that provides easy visibility of the ultrasound image and medical device in real time; and a device that is adapted for releasably fastening an invasive medical device to a probe or imaging device so as to reduce incidences of displacement of the medical device within the patient's body when the medical device is separated from the probe or medical device.